Co-owned U.S. Pat. No. 3,923,183 discloses a plastic bottle for sterile medical liquids with a dispensing outlet sealed by a removable closure cap. The cap is threaded upon the neck of the bottle and an annular rib projecting downwardly from the undersurface of the cap engages the annular top surface of the neck to maintain a hermetic seal between the parts.
While such a seal is effective, it is difficult and relatively expensive to form in production. The closure cap is injection molded of plastic material and should any air become entrapped in the mold, especially in that portion of the mold defining the sealing rib, the resulting product may form an imperfect seal with the neck of the bottle. Since the rib is of small dimensions, even a dimensional variation that cannot be readily detected with the naked eye may render a cap commercially unsatisfactory. Should such variations go undetected during early stages of production, the result may be the expensive and wasteful rejection of bottles and their contents late in production after filling and final sterilizing.
Inadequate sealing may also be caused by other factors. Thus, the thermoplastic bottles are blow molded and, as a final step in their formation, the plastic is cut off to form the annular top surfaces of the bottle necks. Flash tends to be formed along the outer edge of that surface and, should the flash later become trapped beneath a sealing rib when the closure is threaded into place, a leak path may be formed.